Web Content Accessibility Guidelines
HCI No Comments »Introduction
Accessibility is about reaching the widest possible audience. Web accessibility exploits the full power and flexibility of the Web to ensure maximum access to information, regardless of a users ability or disability, their environment or the devices they use.
Disabilities Communities
Blindness
Blindness involves a substantial, uncorrectable loss of vision in both eyes.
To access the Web, many individuals who are blind rely on screen readers — software that reads text on the screen (monitor) and outputs this information to a speech synthesizer and/or refreshable Braille display. Some people who are blind use text-based browsers such as Lynx, or voice browsers, instead of a graphical user interface browser plus screen reader. They may use rapid navigation strategies such as tabbing through the headings or links on Web pages rather than reading every word on the page in sequence.
Access Barriers:
- Images that do not have alternative text
- Complex images (e.g., graphs or charts) that are not adequately described
- Video that is not described in text or audio
- Tables that do not make sense when read serially (in a cell-by-cell or “linearized” mode)
- Frames that do not have “NOFRAME” alternatives, or that do not have meaningful names
- Forms that cannot be tabbed through in a logical sequence or that are poorly labelled
- Browsers and authoring tools that lack keyboard support for all commands
- Browsers and authoring tools that do not use standard applications programmer interfaces for the operating system they are based in
- Non-standard document formats that may be difficult for their screen reader to interpret
Low Vision
There are many types of low vision (also known as “partially sighted” in parts of Europe), for instance poor acuity (vision that is not sharp), tunnel vision (seeing only the middle of the visual field), central field loss (seeing only the edges of the visual field), and clouded vision.
Access Barriers:
- Web pages with absolute font sizes that do not change (enlarge or reduce) easily
- Web pages that, because of inconsistent layout, are difficult to navigate when enlarged, due to loss of surrounding context
- Web pages, or images on Web pages, that have poor contrast, and whose contrast cannot be easily changed through user override of author style sheets
- Text presented as images, which prevents wrapping to the next line when enlarged
- Also many of the barriers listed for blindness, above, depending on the type and extent of visual limitation
Color blindness
Color blindness is a lack of sensitivity to certain colors. Common forms of color blindness include difficulty distinguishing between red and green, or between yellow and blue. Sometimes color blindness results in the inability to perceive any color.
To use the Web, some people with color blindness use their own style sheets to override the font and background color choices of the author.
Access Barriers:
- Color that is used as a unique marker to emphasize text on a Web site
- Text that inadequately contrasts with background color or patterns
- Browsers that do not support user override of authors’ style sheets
Deafness
Deafness involves a substantial uncorrectable impairment of hearing in both ears. Some deaf individuals’ first language is a sign language, and they may or may not read a written language fluently, or speak clearly.
To use the Web, many people who are deaf rely on captions for audio content. They may need to turn on the captions on an audio file as they browse a page; concentrate harder to read what is on a page; or rely on supplemental images to highlight context.
Access Barriers
- Lack of captions or transcripts of audio on the Web, including webcasts
- Lack of content-related images in pages full of text, which can slow comprehension for people whose first language may be a sign language instead of a written/spoken language
- Lack of clear and simple language
- Requirements for voice input on Web sites
Motor disabilities
Motor disabilities can include weakness, limitations of muscular control (such as involuntary movements, lack of coordination, or paralysis), limitations of sensation, joint problems, or missing limbs. Some physical disabilities can include pain that impedes movement. These conditions can affect the hands and arms as well as other parts of the body.
To use the Web, people with motor disabilities affecting the hands or arms may use a specialized mouse; a keyboard with a layout of keys that matches their range of hand motion; a pointing device such as a head-mouse, head-pointer or mouth-stick; voice-recognition software; an eye-gaze system; or other assistive technologies to access and interact with the information on Web sites. They may activate commands by typing single keystrokes in sequence with a head pointer rather than typing simultaneous keystrokes (”chording”) to activate commands. They may need more time when filling out interactive forms on Web sites if they have to concentrate or maneuver carefully to select each keystroke.
Access Barriers
- Time-limited response options on Web pages
- Browsers and authoring tools that do not support keyboard alternatives for mouse commands
- Forms that cannot be tabbed through in a logical order
Speech disabilities
Speech disabilities can include difficulty producing speech that is recognizable by some voice recognition software, either in terms of loudness or clarity.
To use parts of the Web that rely on voice recognition, someone with a speech disability needs to be able to use an alternate input mode such as text entered via a keyboard.
Access Barriers
- Web sites that require voice-based interaction and have no alternative input mode
Cognitive and neurological disabilities
Dyslexia, dyscalculia
Individuals with dyslexia or dyscalculia (sometimes called “learning disabilities” in the U.S.) may have difficulty processing written language or images when read visually, or spoken language when heard, or numbers when read visually or heard.
To use the Web, people with learning disabilities may rely on getting information through several modalities at the same time. For instance, someone who has difficulty reading may use a screen reader plus synthesized speech to facilitate comprehension, while someone with an auditory processing disability may use captions to help understand an audio track.
Access Barriers
- Lack of alternative modalities for information on Web sites, for instance lack of alternative text that can be converted to audio to supplement visuals, or the lack of captions for audio
Attention deficit disorder
Individuals with attention deficit disorder may have difficulty focusing on information.
To use the Web, an individual with an attention deficit disorder may need to turn off animations on a site in order to be able to focus on the site’s content.
Access Barriers
- Distracting visual or audio elements that cannot easily be turned off
- Lack of clear and consistent organization of Web sites
Intellectual impairments
Individuals with impairments of intelligence (sometimes called “learning disabilities” in Europe; or “developmental disabilities” or “mental retardation” in the United States) may learn more slowly, or have difficulty understanding complex concepts. Down Syndrome is one among many different causes of intellectual impairments.
To use the Web, people with intellectual impairments may take more time on a Web site, may rely more on graphics to enhance understanding of a site, and may benefit from the level of language on a site not being unnecessarily complex for the site’s intended purpose.
Access Barriers
- Use of unnecessarily complex language on Web sites
- Lack of graphics on Web sites
- Lack of clear or consistent organization of Web sites
Memory impairments
Individuals with memory impairments may have problems with short-term memory, missing long-term memory, or some loss of language.
To use the Web, people with memory impairments may rely on a consistent navigational structure throughout the site.
Access Barriers
- Lack of clear or consistent organization of Web sites
Web Content Accessibility Guidelines
Below are the fourteen Web Content Accessibility Guidelines with a small description of each, taken from http://www.w3.org/TR/WAI-WEBCONTENT
- Provide equivalent alternatives to auditory and visual content - Provide content that, when presented to the user, conveys essentially the same function or purpose as auditory or visual content.
- Don’t rely on colour alone - Ensure that text and graphics are understandable when viewed without colour.
- Use mark-up and style sheets and do so properly - Mark up documents with the proper structural elements. Control presentation with style sheets rather than with presentation elements and attributes.
- Clarify natural language usage - Use mark-up that facilitates pronunciation or interpretation of abbreviated or foreign text.
- Create tables that transform gracefully - Ensure that tables have necessary mark-up to be transformed by accessible browsers and other user agents.
- Ensure that pages featuring new technologies transform gracefully - Ensure that pages are accessible even when newer technologies are not supported or are turned off.
- Ensure user control of time-sensitive content changes - Ensure that moving, blinking, scrolling, or auto-updating objects or pages may be paused or stopped.
- Ensure direct accessibility of embedded user interfaces - Ensure that the user interface follows principles of accessible design: device-independent access to functionality, keyboard operability, self-voicing, etc.
- Design for device-independence - Use features that enable activation of page elements via a variety of input devices.
- Use interim solutions - Use interim accessibility solutions so that assistive technologies and older browsers will operate correctly.
- Use W3C technologies and guidelines - Use W3C technologies (according to specification) and follow accessibility guidelines. Where it is not possible to use a W3C technology, or doing so results in material that does not transform gracefully, provide an alternative version of the content that is accessible.
- Provide context and orientation information - Provide context and orientation information to help users understand complex pages or elements.
- Provide clear navigation mechanisms - Provide clear and consistent navigation mechanisms - orientation information, navigation bars, a site map, etc. - to increase the likelihood that a person will find what they are looking for at a site.
- Ensure that documents are clear and simple - Ensure that documents are clear and simple so they may be more easily understood.
WCAG Priorities
The Web Accessibility Initiative has specified 3 levels of accessibility, known as priorities :
Priority 1
A Web content developer must satisfy this checkpoint. Otherwise, one or more groups will find it impossible to access information in the document. Satisfying this checkpoint is a basic requirement for some groups to be able to use Web documents.
Priority 2
A Web content developer should satisfy this checkpoint. Otherwise, one or more groups will find it difficult to access information in the document. Satisfying this checkpoint will remove significant barriers to accessing Web documents.
Priority 3
A Web content developer may address this checkpoint. Otherwise, one or more groups will find it somewhat difficult to access information in the document. Satisfying this checkpoint will improve access to Web documents.
To be continued…